Make COLOR_CONTROL_BACKGROUND customizable from a theme extension

chrome/browser/themes/browser_theme_pack.cc

Index: chrome/browser/themes/browser_theme_pack.cc
diff --git a/chrome/browser/themes/browser_theme_pack.cc b/chrome/browser/themes/browser_theme_pack.cc
index 70e81a834842847ff7612a322891752d73e20f6c..5dadf7a1d99447acc1429f742dee57a816053e33 100644
--- a/chrome/browser/themes/browser_theme_pack.cc
+++ b/chrome/browser/themes/browser_theme_pack.cc
@@ -49,7 +49,7 @@ namespace {
 // theme packs that aren't int-equal to this. Increment this number if you
 // change default theme assets or if you need themes to recreate their generated
 // images (which are cached).
-const int kThemePackVersion = 42;
+const int kThemePackVersion = 43;
 
 // IDs that are in the DataPack won't clash with the positive integer
 // uint16_t. kHeaderID should always have the maximum value because we want the
@@ -266,6 +266,7 @@ const size_t kTintTableLength = arraysize(kTintTable);
 
 // Strings used by themes to identify colors in the JSON.
 StringToIntTable kColorTable[] = {
+  { "control_background", ThemeProperties::COLOR_CONTROL_BACKGROUND },
   { "frame", ThemeProperties::COLOR_FRAME },
   { "frame_inactive", ThemeProperties::COLOR_FRAME_INACTIVE },
   { "frame_incognito", ThemeProperties::COLOR_FRAME_INCOGNITO },